This invention relates to electrically conductive transparent tin oxide coatings and, more particularly, to an improved method for rendering transparent substrates such as windows and the like electrically conductive with a transparent coating of tin oxide sol.
In order to impart electrical conductivity to substrates, thin metallic films or conductive inorganic oxide coatings have heretofore been deposited on the surface of the substrate by the vapor phase method, such as CVD method, PVD method and vapor deposition method, etc. It is also known in the art to dope tin oxide with antimony by an evaporative process to impart greater electrical conductivity. However, these techniques suffer from the disadvantage of requiring very large vacuum deposition apparatus or evaporation chambers, or, stated another way, the size or shape of the substrate contemplated to be rendered electrically conductive is limited to the size and shape of the available apparatus for vacuum deposition of the conductive material.
While not intended to represent the state of the art, the following patents cited during the prosecution of the parent case, Ser. No. 08/194,739 warrant brief mention.
U.S. Pat. No. 4,594,182 issued to Hashimoto et al describes another method of imparting electrical conductivity to a substrate utilizing aqueous indium oxide sols doped with tin oxide. However, indium oxide is very expensive compared to tin oxide doped with antimony oxide.
U.S. Pat. No. 4,576,921 describes and claims a tin oxide doped with antimony oxide made into a stable sol with the use of a quaternary ammonium hydroxide suitable for making gels and ceramic materials. However, there is no teaching of any use as coatings and, in fact, because they are prone to crazing, they are not suitable for coatings.
Stated simply, the task of this invention is to provide methods for imparting electrical conductivity to transparent coatings with tin oxide sols, which methods obviate the above-noted disadvantages of the prior techniques.